I. Field of the Invention
The present invention relates to an electrolytic cell of the type used in closed-loop water systems for producing chlorine in sufficient quantities to sanitize the water therein.
II. Description of the Prior Art
It is a well known fact that large, open and stagnant bodies of fresh water become unsanitary for human consumption or use after a prolonged period of time due to the growth of bacteria and algea. One commonly accepted solution to this problem is the use of chlorine in small quantities for inhibiting the growth of the bacteria and algae. While the common swimming pool is perhaps the best known example of the chlorinated circulating water system, the same general chlorination system may also be used in other closed water systems such as air conditioners, water purifications systems, food processing plants, laundry water systems, municipal water supplies, etc.
In the common swimming pool the typical chemical treatment requires the frequent addition of small amounts of an unstable alkaline reacting agent, such as sodium or calcium hypochlorite, which chemically decomposes and releases hypochlorous acid, which is the major disinfectant used in sterilizing the water. Unfortunately, the hypochlorites which are added to the water usually are contaminated with hydroxides which result in the undesirable side effect of increasing the alkaline content of the water. This requires the addition of some form of acid in order to control the ph level of the water. The presence of strong sunlight and warm temperatures for extended periods generally accelerates the decomposition of the chlorine within the closed water system, thereby necessitating the addition of the hypochlorite materials, and thus further exacerbating the problem of maintaining the proper chemical balance within the closed water system.
Several previous attempts have been made to eliminate the necessity of periodically adding the hypochlorite material to the body of water. One method requires the use of a sodium chloride (typical salt) material which is added to the water in the swimming pool. A pair of electrodes are then utilized to produce a chemical reaction. Chlorine is generally formed at the anode electrode and combines with the hydrogen present in the water in order to form hydrochloric acid and hypochlorous acid. The positive sodium ions are attracted toward the cathode and join with the water in order to form sodium hydroxide and hydrogen gas. The sodium hydroxide and the hydrochloric acid recombine to produce water and sodium chloride, the two original ingredients, and the chemical process begins again.
This general chemical reaction is well known in the art. For example, Gwynn in U.S. Pat. No. 3,479,275, discloses the use of an electrolytic cell formed from a transparent casing which encloses a plurality of electrodes in the form of generally parallel spaced plates. The saline solution is pumped between the plates which are energized with a d.c. voltage potential in order to promote the electrolysis action described above. Gwynn periodically reverses the voltage potential across the electrodes in order to prevent the deposition of calcium or other such materials upon the electrodes. While this type of system is chemically effective, the proper functioning of the electrodes requires that they be manufactured from expensive metals such as the noble metals consisting of platinum, rhodium, iridium, osmium and palladium. These metals are both expensive and somewhat difficult to work with, and therefore are not economically well suited for large scale production. For additional background material see also the discussion of non-corroding electrodes as described by Tirrell in U.S. Pat. No. 3,117,023.
Another typical electrolytic system for chlorinating swimming pool water is disclosed by Kirkham in U.S. Pat. No. 3,669,857. This system utilizes a cation selective membrane for separating the two electrodes. While this type of system is chemically effective, it is also expensive to produce and maintain, thereby being at a serious competitive disadvantage with other similar, less expensive and equally effective systems.
Another electrolytic cell for chlorine production is described by Colvin in U.S. Pat. No. 3,476,675. This electrolytic cell again uses flat, porous plates which suffer from the same economic and manufacturing limitations as previously described. In U.S. Pat. No. 3,378,479, Colvin discloses the use of a metal screen mesh as the anode of the electrolytic device. However, the cathode of the electrolytic device is formed from a flat ribbon with a relatively large surface area. Both the cathode and the anode of the electrolytic cell require large surface areas which correspond to increased expenditures for the noble metals required.
The following inventors have attempted to refine this electrolytic process, and to some degree have succeeded in reducing the costs of producing an efficient electrolytic cell. See for example Slater in U.S. Pat. No. 1,397,239, Leslie in U.S. Pat. No. 2,820,701, Gray in U.S. Pat. No. 3,481,857, Copper in U.S. Pat. No. 3,390,065, Colvin in U.S. Pat. No. 3,378,479 and Krane in U.S. Pat. No. 3,458,414. Other related disclosures are contained in U.S. Pat. No. 3,917,520 to Katz, U.S. Pat. No. 3,117,023 to Tirrell and U.S. Pat. No. 3,963,592 to Lindstrom.
While the present invention utilizes the same basic chemical process as described in the preceding references, the present invention uses special electrodes and a special housing for the electrodes, neither of which are disclosed in any of the prior art references. Various other features of the present invention add to the highly efficient operation of the electrolysis system as well as reducing costs of production and increasing reliability.